Seasonal variation in carbon dioxide exchange over a 200-year-old Chinese broad-leaved Korean pine mixed forest

Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy-covariance technology was applied to investigate the long-term carbon exchange over a 200-year-old Chinese broad-leaved Korean pine mixed forest of Forest Ecosystem Open Research Station of Changbai Mountains (1288280E and 428240N, Jilin Province, PR China), Chinese Academy of Sciences, since August 2002. This paper reports the result on (1) phase and amplitude of ecosystem CO2 uptake and release and (2) sink/source status on the data obtained with open-path eddy-covariance system and CO2 profile measurement system from August 2002 to August 2003. Corrections due to storage and friction velocity were applied to the eddy carbon flux. Behavior of pressure flux, neglected in common WPL correction, was analyzed to develop acceptable u* range in dormant periods. The ecosystem was a net sink of atmospheric CO2 and sequestered 308 116 g C m 2 during the study period. The estimates of gross carbon gain and loss at this forest were 1432 216 and 1124 181 g C m 2 separately. The seasonal trend of gross primary productivity (FGPP) and respiration (RE) followed closely the change in vegetation absorption index (VAI) and temperature. The summer is the most significant season as far as ecosystem carbon balance is concerned. The net ecosystem exchange (FNEE) during this period was about 298.0 65.2 g C m . The 90 days of summer contributed 67.0% of FGPP, 58.9% of RE of whole year. This study shows that old-growth forest can be strong net carbon sink of atmospheric CO2. There are uncertainties in estimate of annual carbon fluxes with eddy-covariance method. More work on advection and pressure fluxes is warranted. # 2006 Elsevier B.V. All rights reserved.